1. Field of the Invention
This invention pertains to the insulation of electrical wires and more specifically to treating wires intended for carrying electrical current in such a manner in addition to their ordinary insulation that, in the presence of a bare wire exposure and a small electrical current the wires are electrochemically coated and therefore repaired and protected against further electrical shorts that otherwise would be created in such an environment.
2. Description of the Prior Art
Telephone cables normally comprise a large plurality of wires. Each wire is routinely individually insulated by a plastic coating. These wires in pairs and sometimes in greater number are then wrapped in paper or otherwise to form a second layer of insulation. Finally, the double insulated wires are then enclosed in a plastic jacket or sheath. A petroleum gel is often pressure forced into the end of the cable to help form a moisture barrier.
In use, the wires, through switching equipment and the like, are connected in their respective pairs to one or more small dc power sources to provide the transmission current that is required and eventually to the telephone terminal equipment, namely, one or more telephone transmitters at one end or location and one or more telephone receivers at the other.
In spite of all of the insulation protection afforded, as noted above, nevertheless, all too often, moisture does get into the cable and into the porous intrusions or even breaks in the insulation and causes a conductive path through the moisture from wire to wire. When this happens, the wires either short out altogether or crosstalk is established, thereby disrupting the telephone communications.
In order to dry the wires and correct a short or partial short, the section of cable where the problem occurred must first be isolated. The wires are then exposed, a silica gel is sprinkled into the area and a blow dryer is used to finish the drying. After the moisture is removed, the exposed or bare wires are then rewrapped or spliced and the cable resealed. All of the above is not only messy because of the presence of the petroleum gel, but it is time-consuming and expensive.
Moreover, in addition, it is also well-known that once a problem occurs in a cable section and remedied in the above manner, the problem will likely reoccur in the same area. It is believed that this reoccurrence results because of the abrasive nature of the silica gel. This causes the insulation to wear to reexpose the metal wire and permit moisture again to cause shorts.
U.S. Pat. No. 4,308,416 to Herman, et al. describes the use of water-swellable, water-insoluable polymers in the cable or alternatively in the insulation paper to block water penetration and movement within the cable without resulting in cable breakage as a result of polymer swelling. Suitable polymers for this purpose are prepared by crosslinking an olefinically-unsaturated carboxylic acid with an alkyl acrylate and supplied in amounts of 1% to 10% of the void volume of the cable, preferably 2% to 6% of the void volume. Nevertheless, water leakage in the cable that cannot be absorbed will still cause a short to occur through any intrusion or break in the insulation.
It should be further noted that there is not enough polymer supplied to the attached area according to the Herman, et al. technique to cause electrochemical insulation protection to occur. Herman, et al. polymers are present to absorb some moisture and to cause some swelling to block moisture migration. However, the amount of polymer is limited by the constraints of cable size. If any more polymer were used than that taught by Herman, et al., cable breakage would result.
Therefore, it is a feature of the present invention to provide an improved process for protectively electrochemically coating a bare wire so that even in the presence of intrusions or breaks in the normal insulation of the wire, shorts will not occur between that wire and another wire in the cable.
It is another feature of the present invention to provide an improved method of repairing cable wires after a short has occurred that leaves the repaired area better protected against future shorts from occurring than an unrepaired area.